The present invention relates to a deactivatable thyristor, in which the filamentation during the deactivation operation is averted.
Deactivatable thyristors tend to filamentation during the deactivation operation, because they include a very great number of parallel-connected single thyristors. The causes of these filamentations are lateral discontinuities in the component element, which can for instance be due to the finite conductivity of the metallizing on the cathode side, to nonhomogeneous distributions of the dopant profiles and of the substrate service life, to nonhomogeneous pressure contacting, or to nonhomogeneous etched features. Because of the current filamentation, the maximum current that the component element is capable of turning off without destruction is severely reduced.
This filamentation can be reduced considerably by using series resistors, since the voltage drop established along these series resistors counteracts the filamentation. However, care must be taken that this voltage drop not become too great; otherwise the on-state voltage of the component elements rises too sharply. In principle, series resistors can be embodied by depositing polysilicon on the emitter on the cathode side. However, this is technologically complex, and there are narrow limits to the range within which the resistor can be adjusted.
The object of the present invention is to disclose a deactivatable thyristor in which the effects caused by filamentation are largely avoided.
This object is attained with the thyristor having a semiconductor body, with an emitter layer on the anode side, a base layer on the anode side, a base layer on the cathode side, and an emitter layer on the cathode side, in which an electrically insulating insulation layer, which has openings, is present between the emitter layer on the cathode side and a cathode contact applied over it; and in which the dimensions and spacings of these openings are selected such that the insulation layer forms an electrical resistor for reducing current filamentation.
In the thyristor according to the invention, a series resistor is incorporated on the cathode side. The series resistor is formed by a pierced insulation layer between the metallizing on the cathode side, which forms the terminal contact, and the doped semiconductor material of the emitter on the cathode side. The openings in this insulation layer are preferably cylindrical. In a component element comprising silicon, the insulation layer preferably comprises SiO2 or Si3N4, or a layered succession of SiO2 and Si3N4.